Spraying sunflower: pre-emergence and post-emergence

By Nikola Mojsa, MSc in Agricultural Engineering

Pre-emergence spraying of sunflower: straight after sowing

Early on, sunflower grows more slowly than the weeds, so the first herbicide goes on straight after sowing and before emergence (ADAMA Serbia, in Serbian). In conventional hybrids this is the only treatment against broadleaf weeds and some grass weeds. In herbicide-tolerant hybrids the pre-emergence treatment is not essential, but it is advisable (same source). Once sunflower has emerged, the choice of herbicides is very limited (Agrosava, in Serbian), so a missed pre-emergence window is hard to make up for.

Sunflower is more sensitive to soil-acting herbicides than maize, so lower rates are used, and on sandy soils Agrosava advises avoiding them altogether (same source). Your agronomist chooses the product, and the rate for your soil type, from the label.

For pre-emergence spraying we recommend a tractor sprayer, because the product needs to land as close to the soil as possible.

Post-emergence spraying of sunflower: up to which stage

Broadleaf weeds in hybrids tolerant to imidazolinones (IMI) and sulfonylureas (SU) are controlled from emergence up to the third leaf pair. For these hybrids the Šabac agricultural advisory service (PSS Šabac) gives treatment at 1 to 3 leaf pairs (PSSS, Slavica Maksimović, in Serbian), Galenika Fitofarmacija from the second to the third pair (Galenika Fitofarmacija), and ADAMA up to the third pair (ADAMA Serbia).

Grass weeds, Johnson grass above all, are controlled post-emergence in all hybrids. Johnson grass is treated when it reaches 10 to 15 cm (Agromedia, Agneš Balog, in Serbian). If it emerges unevenly, the same source advises a split application: half the rate straight away and the other half 10 to 14 days later.

On temperature, PSS Šabac gives an optimal range of 10 to 25 °C for post-emergence treatment, and higher than recommended rates in dry spells and on weeds that are already well developed (same source).

Weeds in sunflower: Johnson grass, ragweed, pigweed

The most common weeds in sunflower are Johnson grass and other grass weeds (Johnson grass from seed and from rhizomes, foxtail), and among broadleaf weeds ragweed, pigweed, cocklebur and fat hen (ADAMA Serbia, PSSS). ADAMA names ragweed, pigweed, cocklebur and fat hen as the most troublesome, and for ragweed and pigweed it also mentions biotypes resistant to certain active ingredients. That is why the weeds in the field should be checked before you choose a protection programme.

For rhizome weeds, PSS Šabac gives a post-emergence graminicide based on fluazifop-P-butyl, at the rate set on the label.

The hybrid decides which herbicide you may use

Herbicide-tolerant hybrids (IMI hybrids, tolerant to imazamox, and SU hybrids) withstand a herbicide that would kill a conventional hybrid. You know the hybrid technology before sowing, so the herbicide programme should be agreed before sowing, not when the weeds are already coming up.

This has a direct consequence for neighbours: if a herbicide meant for an IMI hybrid drifts onto a neighbour's conventional sunflower, that crop is destroyed.

Spraying sunflower herbicide by drone: when it makes sense

Herbicides come last in our order of treatments. Fungicides, insecticides, biologicals and foliar feeding take priority, followed by desiccation. With herbicides, drift cannot be avoided completely, so we apply them by drone only when two conditions are met at the same time (how wind and flight height affect drift):

• A tractor cannot get into the field, after heavy rain or because the crop has grown too tall.
• The surrounding fields carry the same crop, which that herbicide does not harm.

In sunflower up to the third leaf pair the crop is short, so the reason is usually mud just as the window is closing, not crop height. The second condition is stricter than it sounds: the neighbouring sunflower has to tolerate the same herbicide, and a neighbour's conventional hybrid does not. If maize, soybean, vegetables or an orchard grow next to the field, we do not apply herbicide by drone.

When both conditions are met, the drone only needs the road to the field to dry, and if there is tarmac to the field we can work the same day after heavy rain. In general we work in wind up to 3 to 5 m/s, and with herbicide, following the drone manufacturer's recommendation, only while the wind is below 3 m/s. As with a tractor sprayer, we do not spray in the hottest part of the day. Our agronomist Nikola mixes the product at the field, and you supply the water and the product. On field crops the drone uses 15 to 20 litres of water per hectare; for herbicide, the exact volume is set by the label and your agronomist.

When either condition is not met, a tractor is the better choice: the sprayer runs low and the weeds get a proper soaking. The drone is the right tool for fungicide in sunflower and for pre-harvest desiccation, once the rows have closed (sunflower protection by drone, sunflower desiccation).

Price of drone herbicide spraying in sunflower

Drone spraying costs €25, €22 or €20 per hectare, for areas up to 20 ha, from 20 to 100 ha and over 100 ha, and herbicide is charged the same as other treatments. Contract tractor spraying in Banat costs about €30 per hectare. Travel within 50 km of Opovo is free, and new clients get the first hectare free on a first order of at least 10 ha. Three treatments on the same field in a season get 5% off, and five or more 10%. Check the price for your field in the calculator.